People getting married at 16 did so under the guidance of closely kept family - something that's far less common these days. When the culture was more agrarian and infant death rates were much higher, you started hatching out babies as early as possible while everyone involved is young and resilient. We now have a much, much lower rate of multi-generational households (when that was common, that 16 year old husband was very unlikely to be the one calling the shots about the family business, farm, finances, etc). We're also expecting young people today to be tuned into a LOT more information and complexity than their counterparts from a century ago.